Prior to the renovation, the house did not have air conditioning and was heated with an 80% efficient natural gas forced-air furnace.   A 55% efficient natural gas hot water heater provided hot water.  Natural gas,  just like coal, is a non- renewable fossil fuel and contributes to global warming.

Heating and Cooling the Home

An outside air-to-water 
heat pump and attached refrigerant-to-water heat exchanger provide heated and cooled  liquid solutions of water and glycol.  The heat pump achieves a coefficient of performance (CoP) of 1 to 3.5.  For every one unit of energy put into the pump, 3.5 units of energy are created.  The heat pump extracts heat out of the surrounding air, even if the outside temperature is below freezing.  It transfers that heat to the liquid, which then runs through into the house and used for domestic hot water, radiant heating and forced-air heating.Recurve (formerly Sustainable Spaces) designed and installed a new heating, ventilation, and air conditioning (HVAC) system.

The heated liquid circulates through a heat exchanger located inside the domestic 80-gallon hot water storage tank. The storage tank supplies hot water to the fixtures in the house. The heat pump also provides a chilled liquid solution to a heat exchanger inside the cold-water storage tank. The cold water is re-circulated through the hydronic air handler for forced air-cooling.

Radiant floors are efficient because they heat the people in the room, not the air. The thermostats can be set two degrees lower than forced air systems, without compromising comfort. The liquid is re-circulated back to the heat pump to be reused.
The sunroom on the first level of the house and the upstairs master bathroom are heated with a radiant floor heating system. Hot liquid solution from the heat pump circulates through cross-linked polyethylene tubing (PEX) looped under the floor. The liquid warms the floor to a comfortable temperature. The radiant heat naturally rises and evenly warms all the objects in the room including the floor and walls, which continue to radiate heat. Aluminum transfer plates beneath the tubing keep the temperature across the floor more evenly distributed.

Hydronic air handlers condition the rest of the rooms in the house with an integrated heat recovery ventilator (HRV). The air handler uses a high-efficiency fan to blow fresh air from the heat recovery ventilator across a set of coils. The two sets of coils, one for heating and one for cooling, carry the heated or cooled liquid. The fresh air is warmed or chilled by the coils. The blower moves the now conditioned air through a system of ducts that lead to ceiling, wall and floor registers throughout the house. The liquid in the coils returns to either the heat pump or the cold-water storage tank and is reused.

The new HVAC system creates a comfortable environment by heating, cooling, and venting the air. The highly efficient system transfers heat from warmer to cooler air.